The case of baby Gammy took a twist today when claims emerged that the surrogate boy's biological father has a criminal record for child abuse.

The allegations were made in Australia prompting the boy's Thai surrogate mum to ask for Gammy's twin sister to be returned to her.

Surrogate Pattaramon Chanbua claims she was left to care for Gammy after the Australian man and his wife took their daughter home but abandoned the twin brother because he was born with Down's syndrome and a hole in his heart.

Now Australian Associated Press says it has seen documents that show the man, who is in his 50s but whose name has yet to be made public, was jailed in the late 1990s for sexually molesting two girls under the age of 10 and was sentenced to three years behind bars.

While serving time for that crime, he was charged with six counts of indecency towards a child under the age of 13 and was convicted and sentenced again.

The Nine Network reported that the father's wife confirmed her husband had a conviction.

Pattaramon claims the Western Australia-based couple took their healthy baby girl home from Thailand but left Gammy when they were born six months ago.

She said the couple had asked for Gammy to be aborted when she was seven months pregnant and they had learned of his Down's syndrome.

"I am very worried about my baby girl. I need help from anyone who can bring my girl back to me as soon as possible . . . This news make me sick. I will take care of my twin babies. I will not give her or him to any family that wants a baby."

Since Gammy's plight was revealed more than $200,000 dollars has been pledged to care for the boy, although the Australian government has said it may intervene and make Gammy an Australian citizen so he can get the medical care he needs.

But while Gammy's future is being discussed, the case has shone a spotlight onto the reality of global surrogacy and the rules governing the practice have been called into question.

Australia's immigration minister, Scott Morrison, said the legalities surrounding international surrogacy were 'very, very, very murky' and called for regulations to be examined.

He said: "Sure, there are lots of Australians who are desperate to be parents but that can never, I think, sanction what we have just seen here."

Sarah Taylor Jones, part of the UK-based surrogacy support network Surrogacy UK, said complicated international laws were leaving children and parents vulnerable.

She said: "It was a disaster waiting to happen, and I was frankly just surprised something like this hasn't happened before.

"International surrogacy is very impersonal and very commercial."

Richard Perrins, a solicitor specialising in surrogacy at Natalie Gamble Associates, told the Guardian that an increasing number of couples were looking for surrogate mothers overseas because of the difficulty in finding one in their own country.

In the UK surrogacy is legal, but a couple can only pay 'reasonable expenses' to a surrogate mother.

Mr Perrins said: "There is a push for more regulation in this area, because if it was clearer where people stand both parties would be more at ease."

He said Gammy's case was rare, and added. "In general, people have very positive outcomes from surrogacy. More often than not, it doesn't go wrong."

Rules on surrogacy vary from country to country. The practice is banned in many countries including Germany, Italy, France and Sweden. In other countries, such as the UK and Australia, the laws are more complex.

In Australia it is illegal to pay a woman to carry a baby, although medical costs and reasonable expenses can be paid.

If an altruistic surrogate cannot be found couples with the means to do so from some states can travel overseas to pay a surrogate, but the Australian Capital Territory, New South Wales and Queensland have banned residents from doing so.

In the UK it is legal to use a surrogate mother, but couples can only pay reasonable expenses, leading to a shortage of UK surrogates.

Using a foreign surrogate is not explicitly outlawed but a couple bringing a child born by a surrogate into the UK must apply for a parental order to have parental rights.

According to Families Through Surrogacy, paying for a woman to carry a child is legal in about 19 US states, which have laws recognising compensated surrogacy.

Another 10 allow unpaid surrogacy. Such laws tend to enable would-be parents to change the birth certificate of the child and gain legal recognition of parenthood.

All children born via surrogacy in the US are eligible for a US passport, regardless of the citizenship of their parents.

India is a popular destination for parents looking for a surrogate mother as commercial surrogacy is legal and the costs are significantly lower than in developed nations.

This has created a rising demand for Indian surrogate mothers, according to Families Through Surrogacy, and has turned 'surrogacy tourism' into a billion dollar industry.

In Thailand, the government last month announced a crackdown on commercial surrogacy and said surrogates must be a blood relative.

According to FTS some Thai-based surrogacy websites have been taken off-line so operators to review content to ensure it complies with Thai medical guidelines and avoid prosecution.